The forward advancing of a workpiece, specifically a bar, through a lathe to permit sequential working operations to be performed has generally been accomplished utilizing a push-type mechanism, commonly referred to as a bar pusher. The standard bar pusher typically comprises a sleevelike element formed substantially as a collet, that is, the sleeve has slots extending axially inwardly from one end thereof so that the sleeve defines a plurality of resilient spring fingers. The sleeve is typically constructed of steel and hence the spring fingers deflect to permit engagement with a bar or workpiece when advancing of same is desired. This standard bar pusher is normally positioned on the rearward or back side of the lathe collet so as to engage the workpiece and push same forwardly. However, due to the size and mass of the bar being advanced, which bar may be as much as 12 feet in length, each stoppage of the pusher results in imposition of a substantial impact force on the lathe, and hence this significantly increases the wear and tear on the lathe.
To avoid use of the spring steel collet as a pusher, another bar pusher has been developed which utilizes a steel-capped rubber insert captivated within a finger sleeve, which rubber insert is squeezed to deform same into gripping engagement with the bar so as to permit gripping engagement therewith and hence advancing of the bar. With this known pusher, as manufactured by Green (see U.S. Pat. No. 2,426,200), the pusher is again positioned on the back side of the collet. Also, this pusher is of undesirable axial length, and cannot be easily manually adjusted.
While the use of bar pushers for advancing the bar or workpiece has been conventional and well known for many years, nevertheless the known bar pushers do cause excessive wear and tear on the machine, and are relatively expensive in view of the requirement that they be positioned on the back side of the collet. Further, many of the known bar pushers have not possessed any significant adjustability with respect to the gripping force which is imposed on the bar during the advancing thereof.
In an attempt to overcome the disadvantages associated with conventional bar pushers, one manufacturer, Advance Tool Systems, has developed a bar puller which mounts on the front side of the machine. In particular, this known bar puller mounts on the turret of a lathe, and hence can be advanced into engagement with the bar, and then retracted to permit advancing of the bar stock. With this known bar puller, there is provided a straight shank which is adapted for engagement with the turret, which shank has a threaded holder on one end which engages the threaded end of a standard split spring-type pusher sleeve, which sleeve in this instance is used as a puller. This known puller, however, possesses many of the same disadvantages associated with conventional pushers. That is, it again utilizes a split metal sleeve so as to define spring fingers, and the arrangement hence does not possess the desired level of adjustability. Also, it will readily scratch or mar soft or ground materials.
Accordingly, it is an object of this invention to provide an improved bar puller adapted for mounting on machines, specifically numerically controlled lathes, for advancing a bar or workpiece, which puller overcomes many of the disadvantages associated with known pushers and pullers.
More specifically, this invention relates to an improved puller which is structurally and operationally simple, is compact in size, particularly of short axial extent, is adjustable (including manually) to readily accommodate bars having a substantial range of sizes, is capable of efficiently advancing the bar or workpiece without subjecting the machine to excessive impact loads or stresses, is capable of operating for long periods of time while experiencing only minimum wear, and is relatively inexpensive to construct.
The improved bar puller of this invention specifically includes a holder which comprises a cuplike support having a shank projecting axially therefrom, which shank is adapted for engagement within a machine tool support, such as a lathe turret. The cuplike holder has a bore which opens outwardly through one end thereof, and a gripping unit is removably positioned within this bore. The gripping unit comprises an elastomeric sleeve having metal end plates mounted on opposite ends thereof, one of which bears against a shoulder disposed at the inner end of the bore, and the other of which projects outwardly beyond the open end of the bore. An actuator is threadably engaged on the free end of the holder and has a radially inwardly projecting flange which engages the end plate associated with the exposed end of the grip unit. By suitably adjustably threading the actuator onto the holder, the grip unit is axially compressed so as to effect elastomeric deformation of the sleeve to enable it to grippingly engage a bar which can be inserted into the opening defined by the grip unit.
With the improved bar puller of this invention, the actuator can be suitably adjusted so as to regulate and control the deformation of the grip unit, and hence the gripping engagement on the bar, from outside the machine both when the machine is running and when stopped. Further, this grip unit will successfully engage and advance even short bars without the need for an extra pusher bar, and when wear of the grip unit is experienced, then the actuating nut can be removed from the holder so that the grip unit can be axially reversed within the holder so as to extend the useful life thereof.
With this improved bar puller, proper gripping can be achieved even with bars of extremely small cross-sectional area, such as bars having a diameter of one-fourth inch or smaller. The bar puller can also be properly tightened for gripping engagement with bars having a noncircular cross section, such as hexagonal bars. In one modification of this bar puller, the bar puller is provided with an anti-friction bearing between the gripping unit and the support shank so as to permit a bar to be utilized in conjunction with a rotating spindle without requiring complete stoppage of the spindle rotation.
These and other objects of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.